128 AN INTRODUCTION TO ZOOLOGY. 



The cell constantly changes its shape, throwing out irregular 

 prolongations of its substance, called pseudopodia. Food 

 particles may be absorbed through any portion of the semi- 

 fluid ectosarc ; a " vacuole of ingestion " appears round them 

 as they pass in, and a similar "vacuole of excretion" when 

 the undigested residue passes out. In most of these char- 

 acters it is closely resembled by many forms of animal cell, 

 which are therefore spoken of as amoeboid or amoebiform. 



Position as a type of its suh-hingdom. Many species of its 

 own class, which differ considerably in the adult form, have 

 young stages which are almost indistinguishable from Amoeba 

 except in size ; the young stages (myxopods) of some organisms 

 in the class Infusoria also resemble it in many respects. 



Hahlts. Amoeba is a microscopic fresh-water organism 

 found crawling on weeds in stagnant and muddy water. It 

 eats both animal and vegetable organisms, digesting the pro- 

 teids only, and rejecting the starch and fat. 



Development. The young Amoebce produced by fission are 

 exactly like the old ones in everything but size. 



Place in classification. Sub-kingdom Protozoa ; class 

 Rhizopoda ; order Foraminifera ; sub-order Lobosa or 

 Amoibiformes ; genus Amceha. 



Detailed description. See Huxley and Martin's " Practical 

 Biology"; Parker's "Elementary Biology"; and Howes' 

 " Atlas of Practical Elementary Biology." 



The class Infusoeia are Protozoans more or less resem- 

 bling the Bell Animalcule, Vorticella (various species, micro- 

 stomum, etc.). See flg. 122, p. 303. 



Vorticella is a stalked bell-shaped unicellular organism with 

 a contractile vacuole and large horseshoe-shaped nucleus (endo- 

 plast). It is more highly specialized than Amoeba, affording 

 an instance of the highest degree of differentiation of parts 

 which is obtained by single cells. It cannot, like Amceba, 

 throw out pseudopodia, or ingest food at any point; it pos- 



